Head mounted display and optical position adjustment method of the same

ABSTRACT

Disclosed herein is an optical position adjustment method of a head mounted display, the head mounted display including (a) an eyeglass type frame worn on the head of a viewer, and (b) two image display devices for the right and left eyes attached to the frame, and each of the image display devices including (A) an image forming device, and (B) an optical device adapted to receive, guide and emit light emitted from the image forming device, wherein the optical position adjustment method includes the step of: controlling an image signal that is supplied to the image forming device making up at least one of the image display devices so as to control the position of the image displayed on the optical device making up at least one of the image display devices and adjust the mutual positions of the two images.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/458,354, entitled “HEAD MOUNTED DISPLAY AND OPTICAL POSITIONADJUSTMENT METHOD OF THE SAME,” filed Aug. 13, 2014, which is acontinuation of U.S. patent application Ser. No. 13/078,147, now U.S.Pat. No. 8,907,865, entitled “HEAD MOUNTED DISPLAY AND OPTICAL POSITIONADJUSTMENT METHOD OF THE SAME,” filed on Apr. 1, 2011, which claims thebenefit under 35 U.S.C. §119 of the filing date of Japanese PatentApplication JP 2010-089494, filed on Apr. 8, 2010. Each of the foregoingdocuments is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a head mounted display (HMD) and anoptical position adjustment method of the head mounted display.

2. Description of the Related Art

A virtual image display device (image display device) is well known, forexample, from Japanese Patent Laid-Open No. 2006-162767 that is designedto allow for the viewer to view a two-dimensional image, formed by animage forming device, as an enlarged virtual image by means of a virtualimage optics.

As illustrated in a conceptual diagram shown in FIG. 1, an image displaydevice 100 includes an image forming device 111, collimating optics 112and optical device (light guiding section) 120. The image forming device111 includes a plurality of pixels arranged in a two-dimensional matrix.The collimating optics 112 shapes light, emitted from the pixels of theimage forming device 111, into parallel beams. The optical device 120receives light shaped into parallel beams by the collimating optics 112,guides the beams therein and emits them. The optical device 120 includesa light guide plate 121, first deflection section 130 (e.g., made up ofa single layer of an optical reflecting film) and second deflectionsection 140 (e.g., made up of a multi-layer optical reflecting filmhaving a multi-layer stacked structure). The light guide plate 121 emitsincident light that has propagated therein by total reflection. Thefirst deflection section 130 reflects incident light on the light guideplate 121 in such a manner that incident light is totally reflected inthe light guide plate 121. The second deflection section 140 causeslight, that has propagated in the light guide plate 121 by totalreflection, to be emitted from the light guide plate 121. When used tomake up an HMD, the image display device 100 configured as describedabove contributes to reduced weight and size of the HMD.

Alternatively, a virtual image display device (image display device)using a holographic diffraction grating is well known, for example, fromJapanese Patent Laid-Open No. 2007-94175 that is designed to allow forthe viewer to view a two-dimensional image, formed by an image formingdevice, as an enlarged virtual image by means of a virtual image optics.

As illustrated in a conceptual diagram shown in FIGS. 12A and 12B, animage display device 300 basically includes the image forming device 111and collimating optics 112 and an optical device (light guiding section)320 adapted to receive light displayed on the image forming device 111for displaying an image and guide it onto an eye 41 of the viewer. Here,the optical device 320 includes a light guide plate 321 and first andsecond diffraction grating members 330 and 340 each made up of areflection volume holographic diffraction grating provided on the lightguide plate 321. The collimating optics 112 receives light emitted fromthe pixels of the image forming device 111 and shapes it into parallelbeams which are then received by the light guide plate 321. The parallelbeams strike a first surface 322 of the light guide plate 321 and areemitted therefrom. On the other hand, the first and second diffractiongrating members 330 and 340 are attached to a second surface 323 of thelight guide plate 321 that is parallel to the first surface 322 thereof.

Still alternatively, a stereoscopic display is well known from JapanesePatent Laid-Open Nos. Hei 08-322004 and Hei 08-211332 that is designedto display, on the display surface of the display section, an image insuch a manner as to permit stereoscopic viewing. The stereoscopicdisplay device disclosed in Japanese Patent Laid-Open No. Hei 08-322004includes a section adapted to electrically move the image displayed onthe display device horizontally so that the convergence angle roughlymatches the visibility in real time. On the other hand, the stereoscopicimage reproduction device disclosed in Japanese Patent Laid-Open No. Hei08-211332 is designed to provide a stereoscopic image by takingadvantage of binocular parallax and includes a convergence angleselection section and control section. The convergence angle selectionsection sets the convergence angle for viewing a reproduced image. Thecontrol section controls the relative reproduction positions of the leftand right images based on the information about the selected convergenceangle.

SUMMARY OF THE INVENTION

Incidentally, if the viewer frequently puts on and takes off a frame1010 in a repeated fashion as illustrated in FIGS. 21A and 21B, templeportions 1013, for example, may expand in the direction shown by anarrow A. This causes a front portion 1011 of the frame 1010 to deform inthe direction shown by an arrow B. In the event of such a phenomenon,the spatial position of the image (virtual image) (virtual imageposition) formed by light emitted from the optical device 120 or 320changes.

In the case of a binocular head mounted display in particular, such aphenomenon changes the convergence angles of the left and right images.This leads to discrepancy in preadjusted spatial distance to the virtualimage, causing fatigue to the viewer during viewing. That is, in FIG.21B, where the spatial position where the preadjusted centers of theleft and right virtual image screens intersect each other is “C,” thespatial position where the centers of the left and right virtual imagescreens intersect each other moves to “D” as a result of the deformationof the front portion 1011 of the frame 1010, thus resulting in a largerconvergence angle. It should be noted that such a change in convergenceangle may also occur due, for example, to impact on the binocular headmounted display or change over time.

On the other hand, the optical adjustment of the two image displaydevices 100 or 300 for the right and left eyes is necessary duringmanufacture of a binocular head mounted display. That is, the relativeposition adjustment of the two image display devices 100 or 300 isrequired so as to provide a desired image. However, such an adjustmentis often difficult to achieve.

Japanese Patent Laid-Open Nos. Hei 08-322004 and Hei 08-211332 do notdisclose any specific method to adjust the relative positions of the twoimage display devices 100 or 300 in such a binocular head mounteddisplay in the event of a change in the relative positions thereof dueto a variety of causes or during assembly of a binocular head mounteddisplay.

In light of the foregoing, it is desirable to provide a method toadjust, with ease, the relative positions of two images displayed on twoimage display devices in a binocular head mounted display in the eventof a change in the relative positions of the two image display devicesdue to a variety of causes or during assembly of a binocular headmounted display and the head mounted display.

Optical position adjustment methods of a head mounted display accordingto first to fourth embodiments are intended for use in a head mounteddisplay (binocular head mounted display) including:

(a) an eyeglass type frame worn on the head of the viewer, and

(b) two image display devices for the right and left eyes attached tothe frame, in which each of the image display devices includes:

(A) an image forming device, and

(B) an optical device adapted to receive, guide and emit light emittedfrom the image forming device.

In the optical position adjustment method of a head mounted displayaccording to the first embodiment (hereinafter may be referred to as themethod of the present invention according to the first embodiment), animage signal (input image signal or input image data) is controlled thatis supplied to the image forming device making up at least one of theimage display devices, thus controlling the position of the imagedisplayed on the optical device making up at least one of the imagedisplay devices and thereby adjusting the mutual positions of the twoimages.

In the optical position adjustment method of a head mounted displayaccording to the second embodiment (hereinafter may be referred to asthe method of the present invention according to the second embodiment),firstly, an image displayed on each optical device is captured with anassociated imaging device. Secondly, the displacement of the imageobtained by each of the imaging devices from a reference position isfound. Thirdly, an image signal (input image signal or input image data)is controlled that is supplied to the image forming device making up atleast one of the image display devices so as to eliminate thedisplacement, thus adjusting the mutual positions of the two images.

Further, in the optical position adjustment method of a head mounteddisplay according to the third embodiment (hereinafter may be referredto as the method of the present invention according to the thirdembodiment), an image signal (input image signal or input image data) iscontrolled that is supplied to the image forming device making up atleast one of the image display devices, thus controlling the position ofthe image displayed on the optical device making up at least one of theimage display devices and thereby adjusting the mutual positions of thetwo images. Additionally, based on the distance from the head mounteddisplay to the target, an image signal (input image signal or inputimage data) is further controlled that is supplied to the image formingdevice making up at least one of the image display devices, thusadjusting the convergence angle commensurate with the distance from thehead mounted display to the target.

Still further, in the optical position adjustment method of a headmounted display according to the fourth embodiment (hereinafter may bereferred to as the method of the present invention according to thefourth embodiment), first, an image displayed on each optical device iscaptured with an associated imaging device. Next, the displacement ofthe image obtained by each of the imaging devices from a referenceposition is found. Then, an image signal (input image signal or inputimage data) is controlled that is supplied to the image forming devicemaking up at least one of the image display devices so as to eliminatethe displacement, thus adjusting the mutual positions of the two images.Additionally, based on the distance from the head mounted display to thetarget, an image signal (input image signal or input image data) isfurther controlled that is supplied to the image forming device makingup at least one of the image display devices, thus adjusting theconvergence angle commensurate with the distance from the head mounteddisplay to the target.

It should be noted that, in the method of the present inventionaccording to the first or third embodiment, an image signal (input imagesignal or input image data) supplied to the image forming device toadjust the mutual positions of the two images will be referred to as a“first image signal” for convenience. Further, an image displayed oneach optical device is captured with an associated imaging device in themethod of the present invention according to the second or fourthembodiment. An image signal supplied at this time to the image formingdevice to obtain an image is also a “first image signal.” Still further,in the method of the present invention according to the third or fourthembodiment, an image signal (input image signal or input image data)supplied to the image forming device making up at least one of the imagedisplay devices and controlled based on the distance from the headmounted display to the target will be referred to as a “second imagesignal” for convenience. In the method of the present inventionaccording to the third or fourth embodiment, the image display devicecontrolled by the first image signal and that controlled by the secondsignal may be the same or different image display devices. Stillfurther, in the methods of the present invention according to the firstto fourth embodiments, the image display devices controlled by the firstimage signal may be two image display devices, and the image displaydevices controlled by the second image signal may be two image displaydevices.

In the methods of the present invention according to the first to fourthembodiments, the first image signal is controlled that is supplied tothe image forming device making up at least one of the image displaydevices, thus controlling the position of the image displayed on theoptical device making up at least one of the image display devices andthereby adjusting the mutual positions of the two images. This makes itpossible to optically adjust the two image display devices for the rightand left eyes, that is, adjust the optical positions of the two imagedisplay devices with ease to provide a desired image, for example,during manufacture of a binocular head mounted display. Further, themutual optical positions of the two image display devices can beadjusted without using any special parts or mechanical adjustment, thuscontributing to reduced number of manufacturing steps for the headmounted display and reduced manufacturing cost. Moreover, it is possibleto readily respond to the change in mutual optical positions of the twoimage display devices over time, contributing to significantly reducedadjustment cost and adjustment time. That is, it is possible toelectrically accommodate an assembly error of the head mounted displayand the change in mutual optical positions of the two image displaydevices over time, thus providing the advantageous effects describedabove. Further, it is possible to instantly change the distance to thevirtual image formed by the two optical devices according to thelocation and situation of use. Still further, the viewer can actively orpassively change the distance to the virtual image, thus allowing forthe viewer to view the virtual image at a comfortable position. Further,the head mounted display includes the image display devices, thuscontributing to reduced weight and size of the head mounted display andproviding significantly reduced discomfort while the head mounteddisplay is worn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of an image display device of a headmounted display in example 1;

FIG. 2 is a diagram schematically illustrating the propagation of lightin a light guide plate making up the image display device of the headmounted display in example 1;

FIG. 3 is a schematic diagram of the head mounted display in example 1as seen from above;

FIG. 4 is a schematic diagram of the head mounted display in example 1as seen from the side;

FIG. 5 is a schematic diagram of the head mounted display in example 1as seen from the front;

FIG. 6 is a diagram of the head mounted display in example 1 worn on thehead of the viewer as seen from above (where only the image displaydevices are shown and the frame is not shown);

FIG. 7 is a conceptual diagram of the head mounted display in example 1while being used;

FIG. 8 is a conceptual diagram of the head mounted display in example 1while being used;

FIGS. 9A to 9C are schematic diagrams illustrating the displacement ofimages displayed by the image display devices for the left and righteyes;

FIGS. 10A and 10B are, respectively, a conceptual diagram of a signalformat including an image signal (second image signal) supplied to animage forming device together with distance information from the headmounted display to the target, and a schematic diagram for describingthe adjustment of a convergence angle commensurate with the distancefrom the head mounted display to the target;

FIG. 11 is a conceptual diagram of the image display device of the headmounted display in example 2;

FIGS. 12A and 12B are conceptual diagrams of the image display device ofthe head mounted display in example 3;

FIG. 13 is a conceptual diagram of the image display device of the headmounted display in example 4;

FIGS. 14A and 14B are, respectively, a diagram schematicallyillustrating the propagation of light in the light guide plate making upthe image display device of the head mounted display in example 5, and aconceptual diagram of the arrangement of the light guide plate and othercomponents;

FIG. 15 is a schematic diagram of the head mounted display in example 5as seen from the side;

FIGS. 16A and 16B are, respectively, a diagram schematicallyillustrating the propagation of light in the light guide plate making upthe image display device of the head mounted display in example 6, and aconceptual diagram of the arrangement of the light guide plate and othercomponents;

FIG. 17 is a schematic diagram of the head mounted display in example 7as seen from the front;

FIG. 18 is a schematic diagram of the head mounted display in example 7as seen from above;

FIG. 19 is a schematic diagram of the head mounted display in example 8as seen from above for describing the optical position adjustment methodof the head mounted display according to a third embodiment of thepresent invention;

FIG. 20 is a schematic diagram of one type of the head mounted displayin example 1 as seen from the side; and

FIGS. 21A and 21B are diagrams schematically illustrating the existingimage display device attached to an eyeglass frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although a detailed description will be given below with reference tothe accompanying drawings and based on the preferred embodiments, thepresent invention is not limited to these preferred embodiments. Variousnumbers and materials given in the embodiments are merely illustrative.It should be noted that the description will be given in the followingorder:

1. Description in general of the optical position adjustment method ofthe head mounted displays according to the first to fourth embodiments2. Example 1 (optical position adjustment method of the head mounteddisplays according to the first and third embodiments)3. Example 2 (modification of example 1)4. Example 3 (another modification of example 1)5. Example 4 (modification of example 3)6. Example 5 (modification of examples 1 to 4)7. Example 6 (modification of example 5)8. Example 7 (still another modification of example 1)9. Example 8 (optical position adjustment method of the head mounteddisplays according to the second and fourth embodiments)10. Example 9 (modification of example 8) and others

In the method of the present invention according to the second or fourthembodiment, a reference position can be an imaging position of a subjectin an imaging device obtained when the subject, located at a givenposition forward of two optical devices, is imaged by the imagingdevice.

In the methods of the present invention according to the first to fourthembodiments including the above preferred modes, the adjustment of themutual positions of the two images can be accomplished by an arbitrarycombination of horizontal and vertical movements and rotation of theimage displayed on the optical device making up at least one of theimage display devices. In order to move the image in the mannersdescribed above, it is only necessary to, for example, set aside anon-display portion on the optical device and assign this portion formoving the image.

In the methods of the present invention according to the first to fourthembodiments including the above preferred modes, it is preferred thatthe optical devices should be see-through. More specifically, at leastthe portions of the optical devices for the both eyes of the viewershould preferably be see-through so that the viewer can see the outsidescenery through these portions of the optical devices.

In the method of the present invention according to the third or fourthembodiment including the above-described preferred modes, distanceinformation from the head mounted display to the target can betransmitted to the head mounted display from external equipment inaddition to the image signal (second image signal) supplied to the imageforming device. It should be noted that the distance information needonly be transmitted wirelessly to the head mounted display from externalequipment. Alternatively, the head mounted display can further include adistance measurement device adapted to measure the distance to thetarget from the head mounted display so that the distance informationcan be obtained by the distance measurement device. More specifically,among examples of the distance measurement device are a camera orimaging device with auto-focusing capability (e.g., active distancemeasurement device adapted to irradiate infrared radiation or ultrasoundonto the target and detect the distance according to the time it takesfor the reflected radiation to return or the irradiation angle, or acamera or imaging device with a passive distance measurement device) anda distance measurement device for camera with auto-focusing capability(active distance measurement device). Alternatively, buttons or switchescan be provided on the control device to manually set the distance tothe target from the head mounted display.

Further, in the method of the present invention according to the thirdor fourth embodiment including the above-described preferred modes andconfiguration, a luminance signal of an image to be displayed on theoptical devices can be transmitted to the head mounted display fromexternal equipment in addition to the image signal (second image signal)supplied to the image forming devices. It should be noted that theluminance signal need only be transmitted wirelessly to the head mounteddisplay from external equipment. Alternatively, the head mounted displaycan further include a light reception sensor so that the luminance ofthe image to be displayed on the optical devices can be controlled basedon luminance information of the environment (atmosphere in which thehead mounted display or target is located) obtained by the lightreception sensor. More specifically, among examples of the lightreception sensor are a photodiode and a light reception element forexposure measurement incorporated in the above camera or imaging device.

Still further, in the method of the present invention according to thethird or fourth embodiment including the above-described preferred modesand configurations, the image signal (second image signal) is furthercontrolled that is supplied to the image forming device making up atleast one of the image display devices based on distance from the headmounted display to the target. At this time, the image displayed on theoptical devices by the second image signal can be made up of text. Thesecond image signal used to display text as an image (may be referred toas “text data”) is digital data and need only be prepared in advance bya worker or processing, for example, by a computer. The text data formatdepends on the head mounted display or system used and need only beselected as appropriate.

Still further, in the method of the present invention according to thethird or fourth embodiment including the above-described preferred modesand configurations, the position of a virtual image formed by the twooptical devices (virtual image position) or the distance to the virtualimage formed by the two optical devices from the two optical devices(virtual image distance) can be changed over time. Here, the term“changing over time” refers to changing, every five to ten minutes, thehorizontal position of the image by two pixels in the positive directionor one pixel in the negative direction on the image forming device, forexample, for a period of one to three minutes and then restoring theimage to its original position.

In the method of the present invention according to the third or fourthembodiment, the convergence angle is adjusted commensurate with thedistance from the head mounted display to the target. This brings thedistance between the target and viewer (audience) into agreement, or asclose agreement as possible, with the virtual image distance of theimage displayed by the image display devices, thus allowing for theviewer (audience) watching the target to naturally watch (view) theimage displayed by the image display devices without significantlychanging the focus. In other words, it can be said that so long as sucha condition is achieved, the distance between the target and viewer(audience) is equal to the virtual image distance of the image displayedby the image display devices.

In the present invention, an image signal (input image signal or inputimage data) that allows for a kind of test pattern to be displayed isamong examples of the first image signal. More specifically, ahorizontally extending line, vertically extending line and diagonallyextending line are some of the examples. Here, the term “controlling thefirst image signal” refers to adding a display position correctionsignal to the first image signal. The display position correction signalis added to the first image signal so that the image displayed by theimage display device for the left eye and that displayed by the imagedisplay device for the right eye are superimposed one on top of another,for example, at an infinitely distant place (or desired position). Inthe method of the present invention according to the first or thirdembodiment, for example, the display position correction signal is addedto the first image signal so that the image displayed by the imagedisplay device for the left eye and that displayed by the image displaydevice for the right eye are superimposed one on top of another, forexample, at an infinitely distant place (or desired position) with theworker wearing the head mounted display. Then, the display positioncorrection signal added when the two images are superimposed one on topof another at an infinitely distant place (or desired position) needonly be stored in the control device as a display position controlsignal. In the method of the present invention according to the secondor fourth embodiment, on the other hand, it is only necessary to firstcapture the image displayed on each optical device with the associatedimaging device, next find the displacement of the image positionobtained by each of the imaging devices from the reference position,then find a display position correction signal adapted to eliminate thedisplacement. This display position correction signal need only bestored in the control device as a display position control signal. Then,the position of the image displayed on the optical device making up atleast one of the image display devices is controlled, thus adjusting themutual optical positions of the two image display devices. Morespecifically, it is only necessary to control the position of the imagedisplayed on the optical device making up at least one of the imagedisplay devices so that the image displayed by the image display devicefor the left eye and that displayed by the image display device for theright eye are superimposed one on top of another, for example, at aninfinitely distant place (or desired position). It should be noted that,in the methods of the present invention according to the first to fourthembodiments, the tasks described above need only be performed, forexample, during assembly of the head mounted display, or alternativelyat regular or irregular intervals. Then, the display position controlsignal obtained from the display position correction signal is stored inthe control device (control circuit) and added to the second imagesignal by the control device. The control device can be configured usinga well-known circuit.

In the method of the present invention according to the third or fourthembodiment, the second image signal is further controlled that issupplied to the image forming device making up at least one of the imagedisplay devices based on the distance from the head mounted display tothe target. More specifically, such control need only be addition of aconvergence angle control signal based on distance information and thedisplay position control signal to the second image signal in thecontrol device. This task need only be performed as appropriate, forexample, during viewing of the target, and may be performed by theviewer. As described above, distance information from the head mounteddisplay to the target may be transmitted to the head mounted displayfrom external equipment. Alternatively, the distance information may beobtained by the distance measurement device. Still alternatively,buttons or switches may be provided on the control device to manuallyset the distance to the target from the head mounted display.

In the method of the present invention according to the third or fourthembodiment, the second image signal can be transmitted wirelessly to thehead mounted display. The second image signal is received, for example,by the control device (control circuit) and processed thereby for imagedisplay.

In the image display devices making up the head mounted display(hereinafter simply referred to as the “image display devices of thepresent invention” for the methods of the present invention according tothe first to fourth embodiments including the above-described preferredmodes and configurations (hereinafter may be collectively simplyreferred to as the “method of the present invention”), each of theoptical devices can include:

(a) a light guide plate adapted to emit incident light that haspropagated therein by total reflection;(b) a first deflection section adapted to deflect incident light on thelight guide plate in such a manner that the incident light is totallyreflected in the light guide plate; and(c) a second deflection section adapted to deflect light, that haspropagated in the light guide plate by total reflection, a plurality oftimes so as to cause the light, that has propagated therein by totalreflection, to be emitted from the light guide plate. It should be notedthat the term “total reflection” refers to internal total reflection ortotal reflection in the light guide plate. The same holds true for thedescription given below. On the other hand, the center of the firstdeflection section corresponds to the center of the optical device.

It should be noted that the point where a central beam that has emittedfrom the center of the image forming device and passed through the nodeof the optics on the side of the image forming device enters the opticaldevice is the optical device center, the axis that passes through theoptical device center and is parallel to the axial direction of theoptical device is the X axis, and the axis that passes through theoptical device center and matches the normal of the optical device isthe Y axis. Here, the optics is provided between the imaging formingdevice and optical device to shape light, emitted from the image formingdevice, into parallel beams. The light flux shaped into parallel beamsby the optics enters the optical device, is guided therein and thenemitted.

In the image display device of the present invention, the central beamcan intersect the XY plane at an angle (θ) other than zero degreealthough not limited thereto. This contributes to reduced limitations asto the angle at which to attach the image display device to theattachment portion of an eyeglass frame, thus providing a high degree ofdesign freedom. In this case, it is preferred, for example, from theviewpoint of ease in handling, setting up and attaching the imagedisplay device that the central beam should be included in the YZ plane.On the other hand, the optical axis of the optics can be included in theYZ plane and intersect the XY plane at an angle other than zero degree.Alternatively, the optical axis of the optics can be parallel to the YZand XY planes and pass through a position off the center of the imageforming device. Further, assuming that the XY plane matches thehorizontal plane, the angle θ at which the central beam intersects theXY plane can be an elevation angle. That is, the central beam canproceed toward the XY plane from under the XY plane to strike the XYplane. In this case, it is preferred that the XY plane should intersectthe vertical plane at an angle other than zero degree. Further, it ispreferred that the XY plane should intersect the vertical plane at anangle θ′. It should be noted that five degrees is among examples of themaximum value of θ′ although the maximum value is not limited thereto.Here, the horizontal plane includes the line of sight (“horizontal lineof sight of the viewer”) when the viewer watches the target located inthe horizontal direction (e.g., target at an infinitely distant place inthe horizontal direction, skyline or horizon) and also includes the twoeyes of the viewer on a horizontal level. On the other hand, thevertical plane is vertical to the horizontal plane. Alternatively, whenthe viewer watches the target located in the horizontal direction (e.g.,target at an infinitely distant place in the horizontal direction,skyline or horizon), the central beam that is emitted from the opticaldevice and enters the eyes of the viewer can form a depression angle.Any angle from five to 45 degrees is among examples of the depressionangle with respect to the horizontal plane.

Here, the first deflection section can reflect incident light on thelight guide plate, and the second deflection section can transmit orreflect light, that has propagated in the light guide plate by totalreflection, a plurality of times. In this case, the first deflectionsection can serve as a reflecting mirror, and the second deflectionsection can serve as a half mirror.

In the configuration described above, the first deflection section canbe made, for example, of a metal including an alloy and include a lightreflecting film (kind of mirror) adapted to reflect incident light onthe light guide plate or a diffraction grating (e.g., holographicdiffraction grating film) adapted to diffract light incident on thelight guide plate. Further, the second deflection section can include amulti-layer stacked structure having a number of stacked dielectricfilms, half mirror, polarizing beam splitter or holographic diffractiongrating film. Although the first and second deflection sections areprovided inside the light guide plate (incorporated in the light guideplate), the first deflection section reflects or diffracts the parallelbeam incident on the light guide plate so that the incident parallelbeam is totally reflected in the light guide plate. On the other hand,the second deflection section reflects or diffracts, a plurality oftimes, the parallel beam that has propagated in the light guide plate bytotal reflection, after which the beam is emitted from the light guideplate still in the form of a parallel beam.

Alternatively, the first deflection section can diffract light incidenton the light guide plate, and the second deflection section can diffractlight, that has propagated in the light guide plate by total reflection,a plurality of times. In this case, the first and second deflectionsections can each include a diffraction grating element. Further, thediffraction grating element can include a reflection or transmissiondiffraction grating element. Alternatively, one of the diffractiongrating elements can be a reflection diffraction grating element, andthe other diffraction grating element can be a transmission diffractiongrating element. It should be noted that a reflection volume holographicdiffraction grating is among examples of the reflection diffractiongrating element. The first deflection section including a reflectionvolume holographic diffraction grating may be referred to as the “firstdiffraction grating member” for convenience, and the second deflectionsection including a reflection volume holographic diffraction gratingmay be referred to as the “second diffraction grating member” forconvenience.

A single color (e.g., green) image can be displayed by the image displaydevices an embodiment of the present invention. When a color image isdisplayed, the first or second diffraction grating member can include alaminated structure of P diffraction grating layers made up of areflection volume holographic diffraction grating for the diffractionand reflection of P different types of light having P different (e.g.,P=3 or red, green and blue) wavelength ranges (or wavelengths).Interference fringes for one wavelength range (or wavelength) are formedon each diffraction grating layer. Alternatively, P different types ofinterference fringes can be formed on the first or second diffractiongrating member composed of single-layered diffraction grating layer forthe diffraction and reflection of P different types of light having Pdifferent wavelength ranges (or wavelengths). Still alternatively, thefirst or second diffraction grating member can include a laminatedstructure of diffraction grating layers, each associated with one of theangles of view obtained by dividing the angle of view, for example, intothree equal parts. Adopting these configurations contributes to higherdiffraction efficiency, larger diffraction acceptance angle and optimaldiffraction angle during the diffraction and reflection of light havingdifferent wavelength ranges (or wavelengths) by the first or seconddiffraction grating member.

Among examples of the material of which the first or second diffractiongrating member is made are photopolymer materials. The first and seconddiffraction grating members each including a reflection volumeholographic diffraction grating need only be identical in material andbasic structure to an existing reflection volume holographic diffractiongrating. The term “reflection volume holographic diffraction grating”refers to a holographic diffraction grating adapted to diffract andreflect only positive first order diffracted light. Interference fringesare formed on the diffraction grating member from the inside to thesurface thereof. Such interference fringes need only be formed in thesame manner as in the existing method. More specifically, an object beamis irradiated onto the member (e.g., photopolymer material) making upthe diffraction grating member from a first predetermined direction onone side. At the same time, a reference beam is irradiated onto themember making up the diffraction grating member from a secondpredetermined direction on the other side. It is only necessary torecord the interference fringes formed by the object and reference beamsin the member making up the diffraction grating member. Proper selectionof the first and second predetermined directions and wavelengths of theobject and reference beams provides a desired interference fringe pitchon the surface of the diffraction grating member and a desired slantangle of the interference fringes. The term “slant angle of theinterference fringes” refers to the angle formed between the surface ofthe diffraction grating member (or diffraction grating layer) and theinterference fringes. If the first and second diffraction gratingmembers each include a laminated structure of P diffraction gratinglayers made up of a reflection volume holographic diffraction grating,such a lamination of diffraction grating layers need only beaccomplished by first preparing P diffraction grating layers separatelyand then stacking (bonding) the diffraction grating layers one on top ofanother, for example, with an ultraviolet hardening adhesive.Alternatively, P diffraction grating layers may be prepared by firstpreparing one diffraction grating layer with an adhesive photopolymermaterial and then affixing adhesive photopolymer materials over thediffraction grating layer, sequentially one on top of another.

Alternatively, in the image display devices of the present invention,the optical devices can each include a half mirror adapted to receivelight emitted from the image forming device and emit light toward theeye of the viewer. It should be noted that light emitted from the imageforming device may propagate in the air and enter the half mirror.Alternatively, light may propagate in a transparent member such as glassplate or plastic plate (more specifically, member made of the samematerial as the light guide plate which will be described later) andenter the half mirror. It should be noted that the half mirror may beattached to the image forming device via the transparent member or via amember separate from the transparent member.

In the image display device of the present invention including theabove-described preferred modes and configurations, the image formingdevice can include a plurality of pixels arranged in a two-dimensionalmatrix. It should be noted that the image forming device having such aconfiguration will be referred to as the “image forming device having afirst configuration” for convenience.

Among examples of the image forming device having a first configurationare an image forming device including a reflection spatial lightmodulator and light source, that including a transmission spatial lightmodulator and light source and that including light-emitting elementssuch as organic EL (Electro Luminescence) elements, inorganic ELelements or light-emitting diodes (LEDs). Among others, an image formingdevice including a reflection spatial light modulator and light sourceis preferred. Among examples of the spatial light modulator are a lightbulb, an LCOS (Liquid Crystal On Silicon) or other transmission orreflection liquid crystal display device and a digital micromirrordevice (DMD). A light-emitting element is an example of a light source.Further, the reflection spatial light modulator can include a liquidcrystal display device and polarizing beam splitter. The polarizing beamsplitter reflects part of light from the light source to guide it ontothe liquid crystal display device and transmits part of light reflectedby the liquid crystal display device to guide it onto the optics. Amongexamples of the light-emitting elements making up the light source arered, green, blue and white light-emitting elements. Alternatively, whitelight may be obtained by mixing red, green and blue light emitted fromthe red, green and blue light-emitting elements with light pipes andequalizing the luminance. Among examples of the light-emitting elementsare a semiconductor laser element, solid-state laser and LED. The numberof pixels need only be determined based on the specification required ofthe image display device. Among examples of the pixel count are 320 by240, 432 by 240, 640 by 480, 1024 by 768 and 1920 by 1080.

Alternatively, in the image display device of the present inventionincluding the above-described preferred modes and configurations, theimage forming device can include a light source and a scanning sectionadapted to scan a parallel beam emitted from the light source. It shouldbe noted that the image forming device having such a configuration willbe referred to as the “image forming device having a secondconfiguration” for convenience.

A light-emitting element is among examples of the light source in theimage forming device having a second configuration. More specifically,red, green, blue and white light-emitting elements are among examples ofthe light-emitting element. Alternatively, white light may be obtainedby mixing red, green and blue light emitted from the red, green and bluelight-emitting elements with light pipes and equalizing the luminance.Among examples of the light-emitting element are a semiconductor laserelement, solid-state laser and LED. The number of pixels (virtualpixels) in the image forming device having a second configuration needonly be determined based on the specification required of the imagedisplay device. Among examples of the pixel count are 320 by 240, 432 by240, 640 by 480, 1024 by 768 and 1920 by 1080. On the other hand, if acolor image is displayed, and if the light source includes red, greenand blue light-emitting elements, it is preferred that a cross prismshould be used to combine the colors. Among examples of the scanningsections adapted to scan light emitted from the light sourcehorizontally and vertically are a MEMS (Micro Electro MechanicalSystems) having a two-dimensionally rotatable micromirror, and agalvanomirror.

In the image forming device having a first or second configuration,light is shaped by the optics (optics adapted to shape emitted lightinto parallel beams that may be referred to as the “parallel beamemission optics” and, more specifically, a collimating optics or relayoptics) into a plurality of parallel beams which then enter the lightguide plate. The requirement that light must be parallel beams is basedon the need for optical wavefront information at the time of incidenceof these beams onto the light guide plate to be stored even afteremission from the light guide plate via the first and second deflectionsections. It should be noted that, more specifically, it is onlynecessary to provide, for example, an optical emission section of theimage forming device, for example, at the focal distance position of theparallel beam emission optics in order to generate a plurality ofparallel beams. The parallel beam emission optics is capable ofconverting pixel position information into angle information of anoptics in an optical device. Among examples of the parallel beamemission optics are a convex lens, concave lens, free curved surfaceprism and hologram lens either alone or in combination with each otherto form, as a whole, an optics having positive optical power. Alight-shielding member having an opening may be provided between theparallel beam emission optics and light guide plate to prevent undesiredlight emitted from the parallel beam emission optics from entering thelight guide plate.

The light guide plate has two parallel surfaces (first and secondsurfaces) that extend parallel to the axis of the light guide plate (Xaxis). If the surface on which light is incident is defined as anincidence surface of the light guide plate, and the surface from whichlight is emitted is defined as an emission surface of the light guideplate, both the incidence and emission surfaces of the light guide platemay be made up of the first surface. Alternatively, the incidencesurface of the light guide plate may be made up of the first surface,and the emission surface of the light guide plate may be made up of thesecond surface. Among examples of the material of which the light guideplate is made are glasses including optical glass such as quartz glassand B7 and plastic materials (e.g., PMMA, polycarbonate resins,acryl-based resins, amorphous polypropylene-based resins andstyrene-based resins including AS resin). The shape of the light guideplate is not limited to a flat plate. Instead, the light guiding platemay be curved in shape.

In the present invention, the frame can include a front portion and twotemple portions. The front portion is provided at the front of theviewer. Each of the temple portions is attached to one of the two endsof the front portion to be freely rotatable via a hinge. It should benoted that an ear piece portion is attached to the tip of each of thetemple portions. The image display devices are attached to the frame.More specifically, however, each of the image display devices need onlybe attached, for example, to the temple portion.

Further, in the present invention, nose pads can be attached to theframe. That is, when the head mounted display of the present inventionis viewed as a whole, the assembly made up of a frame and nose pads hasthe same structure as ordinary eyeglasses. There may or may not be a rimportion. The frame can be made of the same material as ordinaryeyeglasses such as metals, alloys, plastics or a combination thereof.The nose pads can have a well-known configuration and structure.

As described earlier, the imaging device can be attached at the centerof the front portion. More specifically, the imaging device includes,for example, a solid-state imaging element and lens. The solid-stateimaging element includes a CCD (Charge Coupled Device) or CMOS(Complementary Metal Oxide Semiconductor) sensor. The wiring from theimaging device need only be connected, for example, to one of the imagedisplay devices (or image forming devices) via the front portion and,further be included in the wiring extending from the image displaydevice (or image forming device).

In the head mounted display of the present invention, it is preferred,from the viewpoint of design and ease of wearing, for example, that thewiring (e.g., signal wires and power wires) from the two image formingdevices should extend externally from the tips of the ear piece portionsvia the inside of the temple and ear piece portions and be connected tothe control device (control circuit). Further, each of the image formingdevices can include a headphone portion so that the wiring for theheadphone portion from each of the image forming devices extends to theheadphone portion from the tip of the ear piece portion via the insideof the temple and ear piece portions. Among examples of the headphoneportion are an inner ear headphone portion and an ear canal headphoneportion. More specifically, it is preferred that the wiring for theheadphone portion should extend from the tip of the ear piece portionand go around and behind the concha to reach the headphone portion.

The head mounted display of the present invention can be used todisplay, for example, subtitles for movies and so on; explanatory textand closed captions relating to an image synchronous with the image;description of the targets and explanatory text for describing thecontent, progress, background and so on of plays, kabuki plays, nohplays, kyogen plays, operas, concerts, ballets, theaters, amusementparks, museums, sightseeing spots, holiday resorts, sightseeing guidesand so on; various descriptions, symbols, signs, marks, emblems, designsand so on relating to the operation, manipulation, maintenance,disassembly and so on of the targets such as various devices; variousdescriptions, symbols, signs, marks, emblems, designs and so on relatingto the targets such as persons or goods; and closed captions. In plays,kabuki plays, noh plays, kyogen plays, operas, concerts, ballets,theaters, amusement parks, museums, sightseeing spots, holiday resorts,sightseeing guides and so on, text in the form of images relating to thetargets need only be displayed by the image display devices at propertimings. More specifically, for example, the second image signal istransmitted to the image display devices according to the progress ofthe movie or play, according to the predetermined schedule, based on thetime allocation and by the manipulation of the worker or under control,for example, of a computer so that images (text) are displayed by theimage display devices. Further, when various descriptions relating tothe targets such as various devices, persons or goods are displayed, itis possible to display such various descriptions relating to the targetssuch as various devices, persons or goods prepared in advance with theimage display devices by providing the imaging device in the headmounted display, capturing images of the targets such as variousdevices, persons or goods by the image capturing devices and analyzingthe content of captured images in the image display devices.Alternatively, the head mounted display of the present invention can beused as a stereoscopic display device.

Then, the second image signal supplied to the image forming devices cancontain not only text data but also, for example, luminance datarelating to text to be displayed, or chromaticity data, or luminancedata and chromaticity data. Luminance data can be that for the luminanceof the predetermined region including the target as seen through theoptical device. The chromaticity data can be that for the chromaticityof the predetermined region including the target as seen through theoptical device. Containing luminance data relating to text as describedabove makes it possible to control the luminance (brightness) of text tobe displayed. Containing chromaticity data relating to text as describedabove makes it possible to control the chromaticity (color) of text tobe displayed. Containing luminance data and chromaticity data relatingto text as described above makes it possible to control the luminance(brightness) and chromaticity (color) of text to be displayed. Whenluminance data for the luminance of the predetermined region includingthe target as seen through the optical device is used, the luminancedata value need only be set so that the higher the luminance of thepredetermined region including the target as seen through the opticaldevice, the higher the luminance value of the image (that is, thebrighter the image is displayed). Further, when chromaticity data forthe chromaticity of the predetermined region including the target asseen through the optical device is used, the chromaticity data valueneed only be set so that the chromaticity of the predetermined regionincluding the target as seen through the optical device and that of theimage to be displayed are in a roughly complementary color relationship.The term “complementary color” refers to colors that are opposite on thecolor circle. Red and green, yellow and purple, and blue and orange arecomplementary colors. Complementary color is also used to refer to acolor that leads to reduced chroma such as white for light and black foran object when a given color is mixed with another color at anappropriate ratio. However, the complementarity of visual effect ofcolors arranged side by side and the complementarity of mixed colors aredifferent. Complementary color is also referred to as a contrastingcolor or opposite color. It should be noted, however, that unlikeopposite color that directly indicates the pairing color, the meaning ofcomplementary color encompasses a slightly broader range. Combiningcomplementary colors is synergistically effective in that the two colorsenhance each other. This is called a complementary color harmony.

Example 1

Example 1 relates to the optical position adjustment methods for a headmounted display according to the first and second embodiments of thepresent invention. FIG. 1 illustrates a conceptual diagram of the imagedisplay device of the head mounted display in example 1. Further, FIG. 2schematically illustrates the propagation of light in the light guideplate making up the image display device of the head mounted display inexample 1. FIG. 3 illustrates a schematic diagram of the head mounteddisplay in example 1 as seen from above. FIG. 4 illustrates a schematicdiagram of the head mounted display in example 1 as seen from the side.Still further, FIG. 5 illustrates a schematic diagram of the headmounted display in example 1 as seen from the front. FIG. 6 illustratesa diagram of the head mounted display in example 1 worn on the head ofthe viewer as seen from above (where only the image display devices areshown and the frame is not shown). FIGS. 7 and 8 illustrate conceptualdiagrams of the head mounted display in example 1 while being used.

The head mounted display in example 1 or each of those in examples 2 to8 which will be described later includes:

(a) an eyeglass frame 10 worn on the head of the viewer, and(b) two image display devices 100, 200, 300, 400 or 500 for the rightand left eyes attached to the frame 10. Each of the image displaydevices 100, 200, 300, 400 or 500 includes:(A) an image forming device 111 or 211, and(B) an optical device (light guiding section) 120, 320 or 520 adapted toreceive, guide and emit light emitted from the image forming device 111or 211. It should be noted that each of the image display devices 100,200, 300, 400 or 500 further includes:(C) an optics 112 or 254 (parallel beam emission optics) adapted toshape light, emitted from the image forming device 111 or 211, intoparallel beams. Here, the optics 112 or 254 is provided between theimage forming device 111 or 211 and optical device 120, 320 or 520. Thelight flux shaped into parallel beams by the optics 112 or 254 entersthe optical device 120, 320 or 520, is guided therein and then emitted.The image forming device 111 or 211 displays a single color (e.g.,green) image. On the other hand, the optical device 120, 320 or 520 issee-through. More specifically, at least the portions (morespecifically, the light guide plate 121 or 321 and a second deflectionsection 140 or 340) of the optical device opposed to the eyes of theviewer are see-through.

It should be noted that, in example 1 or each of examples 2 to 8 whichwill be described later, the point where a central beam CL, emitted fromthe center of the image forming device 111 or 211 and passing throughthe node of the optics 112 or 254 on the side of the image formingdevice, enters the optical device 120, 320 or 520 is an optical devicecenter O. The axis that passes through the optical device center O andis parallel to the axial direction of the optical device 120, 320 or 520is the X axis. The axis that passes through the optical device center Oand matches the normal of the optical device 120, 320 or 520 is the Yaxis. It should be noted that the center of the first deflection section130 or 330 which will be described next is the optical device center O.

Then, the optical device 120 or 320 in example 1 or each of examples 2to 6 which will be described later includes:

(a) the light guide plate 121 or 321 adapted to emit incident light thathas propagated therein by total reflection;(b) the first deflection section 130 or 330 adapted to deflect incidentlight on the light guide plate 121 or 321 in such a manner that theincident light is totally reflected in the light guide plate 121 or 321;and(c) the second deflection section 140 or 340 adapted to deflect light,that has propagated in the light guide plate 121 or 321 by totalreflection, a plurality of times so as to cause the light, that haspropagated therein by total reflection, to be emitted from the lightguide plate 121 or 321.

Here, in example 1, the first and second deflection sections 130 and 140are provided in the light guide plate 121. The first deflection section130 reflects light incident on the light guide plate 121. The seconddeflection section 140 transmits and reflects, a plurality of times,light that has propagated in the light guide plate 121 by totalreflection. That is, the first deflection section 130 serves as areflecting mirror, and the second deflection section 140 serves as ahalf mirror. More specifically, the first deflection section 130provided in the light guide plate 121 is made of aluminum (Al) andincludes a light reflecting film (king of mirror) adapted to reflectincident light on the light guide plate 121. On the other hand, thesecond deflection section 140 provided in the light guide plate 121includes a multi-layer stacked structure having a number of stackeddielectric films. The stacked dielectric films include, for example,TiO₂ films as high dielectric constant films and SiO₂ films as lowdielectric constant films. A multi-layer stacked structure having anumber of stacked dielectric films is disclosed in JP-T-2005-521099.FIG. 1 illustrates six layers of stacked dielectric films. However, thenumber of stacked dielectric films is not limited thereto. A flake madeof the same material as the light guide plate 121 is sandwiched betweenone stacked dielectric film and another. It should be noted that thefirst deflection section 130 reflects (or diffracts) the parallel beamsincident on the light guide plate 121 so that the parallel beamsincident on the light guide plate 121 are totally reflected in the lightguide plate 121. On the other hand, the second deflection section 140reflects (or diffracts), a plurality of times, the parallel beams thathave propagated in the light guide plate 121 by total reflection, afterwhich the beams are emitted, still in the form of parallel beams, to theeye 41 of the viewer from the light guide plate 121.

In order to provide the first deflection section 130, it is onlynecessary to first cut, in the light guide plate 121, a portion 124 onwhich to provide the first deflection section 130 so as to provide, onthe light guide plate 121, a slope on which to form the first deflectionsection 130, next vacuum-vapor-deposit a light reflecting film on theslope and finally bond the first deflection section 130 to the portion124 that has been cut in the light guide plate 121. In order to providethe second deflection section 140, on the other hand, it is onlynecessary to prepare a multi-layer stacked structure having a number ofthe same material (e.g., glass) as the light guide plate 121 and stackeddielectric films (e.g., films that can be formed by vacuum vapordeposition), cut, in the light guide plate 121, a portion 125 on whichto provide the second deflection section 140 so as to form a slope, bondthe multi-layer stacked structure to the slope, and tidy the outershape, for example, by polishing. This provides the optical device 120whose light guide plate 121 incorporates the first and second deflectionsections 130 and 140.

Here, in example 1 or each of examples 2 to 6 which will be describedlater, the light guide plate 121 or 321 made of optical glass or plasticmaterial has two parallel surfaces (first surface 122 or 322 and secondsurface 123 or 323) that extend parallel to the direction (X axis) ofpropagation of light in the light guide plate 121 or 321 by totalreflection. The first surface 122 or 322 and second surface 123 or 323are opposed to each other. The parallel beams enter the first surface122 or 322 that corresponds to a light incidence surface, propagate inthe light guide plate by total reflection and are emitted from thesecond surface 123 or 323 that corresponds to a light emission surface.It should be noted, however, that the light guide plate 121 or 321 isnot limited to this configuration. Instead, the second surface 123 or323 may be a light incidence surface, and the first surface 122 or 322may be a light emission surface.

In example 1 or example 3 which will be described later, the imageforming devices 111 are each an image forming device having a firstconfiguration and include a plurality of pixels arranged in atwo-dimensional matrix. More specifically, each of the image formingdevices 111 includes a reflection spatial light modulator 150 and lightsource 153. The light source 153 includes a light-emitting diode adaptedto emit white light. Each of the image forming devices 111, as a whole,is housed in an enclosure 113 (shown by a dashed-dotted line in FIG. 1or 12A). The enclosure 113 has an opening (not shown) so that light isemitted from the optics (parallel beam emission optics or collimatingoptics) 112 via the opening. The reflection spatial light modulator 150includes a liquid crystal display device (LCD) 151 and polarizing beamsplitter 152. The liquid crystal display 151 is an LCOS liquid crystaldisplay device (LCD) serving as a light bulb. The polarizing beamsplitter 152 reflects part of light from the light source 153 to guideit onto the liquid crystal display device 151 and transmits part oflight reflected by the liquid crystal display device 151 to guide itonto the optics 112. The liquid crystal display device 151 includes aplurality of (e.g., 640 by 480) pixels (liquid crystal cells) arrangedin a two-dimensional matrix. The polarizing beam splitter 152 has awell-known configuration and structure. Non-polarized light emitted fromthe light source 153 strikes the polarizing beam splitter 152. Thep-polarized component passes through the polarizing beam splitter 152,causing this component to be emitted externally. On the other hand, thes-polarized component is reflected by the polarizing beam splitter 152to enter the liquid crystal display device 151 where the component isreflected therein and emitted therefrom. Here, of light emitted from theliquid crystal display device 151, that emitted from the pixels adaptedto display “white” contains a p-polarized component in large quantities,and that emitted from the pixels adapted to display “black” contains ans-polarized component in large quantities. Therefore, of light emittedfrom the liquid crystal display device 151 and striking the polarizingbeam splitter 152, the p-polarized component passes through thepolarizing beam splitter 152 and is guided onto the optics 112. On theother hand, the s-polarized component is reflected by the polarizingbeam splitter 152 back to the light source 153. The optics 112 includes,for example, a convex lens. The image forming device 111 (morespecifically, liquid crystal display device 151) is provided at thefocal distance position of the optics 112 to produce parallel beams.

The frame 10 includes a front portion 11, two temple portions 13 and earpiece portions (also called ear pads) 14. The front portion 11 isprovided at the front of the viewer. Each of the temple portions 13 isattached to one of the two ends of the front portion 11 to be freelyrotatable via a hinge 12. Each of the ear piece portions 14 is attachedto the tip of one of the temple portions 13. Further, nose pads 10′ areattached to the frame 10. That is, the assembly made up of the frame 10and nose pads 10′ basically has the same structure as ordinaryeyeglasses. Still further, each of the enclosures 113 is attached to oneof the temple portions 13 by an attachment member 19. The frame 10 ismade of a metal or plastic. It should be noted that each of theenclosures 113 may be attached to one of the temple portions 13 by theattachment member 19 so as to be freely attachable and detachable.Further, for the viewers who wear their own eyeglasses, each of theenclosures 113 may be attached to one of the temple portions of theireyeglasses by the attachment member 19 so as to be freely attachable anddetachable.

Still further, wiring (e.g., signal wires and power wires) 15 from imageforming devices 111A and 111B extend externally from the tips of the earpiece portions 14 via the inside of the temple portion 13 and ear pieceportion 14 and be connected to a control device (control circuit,control section) 18. Further, each of the image forming devices 111A and111B includes a headphone portion 16 so that wiring 16′ for theheadphone portion 16 from each of the image forming devices 111A and111B extends to the headphone portion 16 from the tip of the ear pieceportion 14 via the inside of the temple portion 13 and ear piece portion14. More specifically, the wiring 16′ for the headphone portion extendsfrom the tip of the ear piece portion 14 and go around and behind theconcha to reach the headphone portion 16. Such a configuration providesan uncluttered head mounted display that does not give any disorderlyimpression in the arrangement of the headphone portion 16 and wiring16′.

An imaging device 17 is attached to a center portion 11′ of the frontportion 11 by a proper attachment member (not shown). The imaging device17 includes a solid-state imaging element and lens (not shown). Thesignal from the imaging device 17 is transmitted to the image formingdevice 111A via wiring (not shown) extending from the imaging device 17.

A description will be given below of the optical position adjustmentmethod of the head mounted display in example 1. It should be noted thatthe following tasks are performed during assembly of the head mounteddisplay, or at regular or irregular intervals, for this opticaladjustment method.

That is, the first image signal (input image signal or input image data)is controlled that is supplied to the image forming device 111A or 111Bmaking up at least one of the image display devices (two image displaydevices 100, 200, 300, 400 or 500 for the right and left eyes in example1). More specifically, an image signal (input image signal or inputimage data) that allows for a kind of test pattern to be displayed as afirst image signal is transmitted in a wired or wireless fashion to thecontrol device 18. Then, the control device 18 processes the first imagesignal for image display, and an image is generated by the image formingdevice 111A or 111B. This image finally reaches the eyes of a worker 40wearing the head mounted display via the optics 112 or 254 and opticaldevice 120, 320 or 520. The test pattern is, for example, a combinationof horizontally, vertically and diagonally extending lines.

Then, the worker 40 moves the images, displayed by the image displaydevices 100, 200, 300, 400 or 500 for the left and right eyes,horizontally and vertically or rotates them via the control device 18,and more specifically, using the switches (not shown) provided on thecontrol device 18 so that the images are superimposed one on top ofanother, for example, at an infinitely distant place (or desiredposition). That is, the images are moved, for example, horizontally orvertically or rotated so that a point “C” in FIG. 21B is at aninfinitely distant place (or desired position). Thus, the first imagesignal is controlled by manipulating the switches provided on thecontrol device 18. That is, a display position correction signal isgenerated by the control device 18 and added to the first image signal.

FIG. 9A schematically illustrates that the images displayed by the imagedisplay devices 100, 200, 300, 400 or 500 for the left and right eyesare horizontally displaced from each other, for example, at aninfinitely distant place (or desired position). FIG. 9B schematicallyillustrates that the images are vertically displaced from each other.FIG. 9C schematically illustrates that the images are displaced fromeach other due to their rotation relative to each other. Here, thediagrams on the right of FIGS. 9A to 9C illustrate the images displayedby the image display device 100, 200, 300, 400 or 500 for the right eye,and those on the left of FIGS. 9A to 9C illustrate the images displayedby the image display device 100, 200, 300, 400 or 500 for the left eye.Further, the dotted lines in the diagrams on the right of FIGS. 9A to 9Cillustrate the images displayed by the image display device 100, 200,300, 400 or 500 for the left eye superimposed on those displayed by theimage display device 100, 200, 300, 400 or 500 for the right eye.

Here, in order to move the test pattern horizontally, it is onlynecessary for the control device 18 to generate a display positioncorrection signal adapted to change the horizontal position of the imagebased on the first image signal by i pixels in the positive or negativedirection. Alternatively, it is only necessary for the control device 18to generate a signal adapted to change the horizontal synchronizingsignal timing by i pixels in the positive or negative direction. Inorder to move the test pattern vertically, on the other hand, it is onlynecessary for the control device 18 to generate a display positioncorrection signal adapted to change the vertical position of the imagebased on the first image signal by j pixels in the positive or negativedirection. Alternatively, it is only necessary for the control device 18to generate a signal adapted to change the vertical synchronizing signaltiming by j pixels in the positive or negative direction. That is, thetest pattern can be moved by delaying or advancing the read position ofthe image memory. Alternatively, the test pattern can be moved bychanging the vertical and horizontal synchronizing signal timings.Further, in order to rotate the test pattern, it is only necessary forthe control device 18 to generate a display position correction signaladapted to rotate the image based on a well-known method.

Then, the display position correction signal obtained when the images,displayed by the image display devices 100, 200, 300, 400 or 500 for theleft and right eyes, are superimposed one on top of another at aninfinitely distant place (or desired position), is stored in the controldevice 18 as a display position control signal. These tasks can beperformed by using the buttons (not shown) provided on the controldevice 18. The image displayed on the optical device 120, 320 or 520making up at least one of the image display devices 100, 200, 300, 400or 500 is controlled, thus adjusting the mutual positions of the twoimages displayed by the image display devices 100, 200, 300, 400 or 500.

Then, the display position control signal, obtained from the displayposition correction signal, is stored in the control device (controlcircuit or control section) 18. A second image signal (e.g., text data)reproduced, for example, by a text data reproduction device 51 or imagedata/text data reproduction device 51′ is transmitted wirelessly to thecontrol device 18 via a text data wireless transmission device 52. Then,the second image signal is processed by the control device 18 for imagedisplay. That is, the control device 18 adds the display positioncontrol signal to the second image signal. Thus, the positions of theimages (various images based on the second image signal) displayed onthe optical device 120, 320 or 520 making up at least one of the imagedisplay devices 100, 200, 300, 400 or 500 can be controlled so that theimages, displayed by the image display devices 100, 200, 300, 400 or 500for the left and right eyes, are superimposed one on top of another atan infinitely distant place (or desired position).

Further, the second image signal (input image signal or input imagedata) is controlled that is supplied to the image forming device 111A or111B making up at least one of the image display devices (two imagedisplay devices 100, 200, 300, 400 or 500 for the right and left eyes inexample 1) based on the distance from the head mounted display to thetarget, thus adjusting the convergence angle commensurate with thedistance from the head mounted display to the target.

Here, the distance information from the head mounted display to thetarget is transmitted to the head mounted display from externalequipment in addition to the image signal (second image signal) suppliedto the image forming device 111A or 111B. FIG. 10A illustrates aconceptual diagram of such a signal format. Then, it is only necessaryfor the control device 18 to generate a signal (convergence anglecontrol signal) adapted to change, based on the distance information,the horizontal position of the image based on the second image signal byk pixels in the positive or negative direction. It should be noted thatit is only necessary to examine, in advance, the extent to which theconvergence angle or virtual image distance changes when the horizontalposition of the image changes by one pixel and store, in the controldevice 18, the relationship therebetween. It should also be noted thatthis signal and three display position control signals, i.e., oneadapted to change the horizontal position of the image by i pixels inthe positive or negative direction, another adapted to change thevertical position of the image by j pixels in the positive or negativedirection, and still another adapted to rotate the image, are added andtransmitted to the image forming device 111A or 111B. Thus, the imagecan be actively moved based on the distance information (or horizontalmovement), thus making it possible to place the virtual image at adesired position.

Alternatively, the head mounted display may further include a distancemeasurement device adapted to measure the distance to the target fromthe head mounted display so that distance information can be obtainedfrom the distance measurement device. For example, an imaging devicewith auto-focusing capability (imaging device having a passive distancemeasurement device) need only be used as an imaging device 17 to serveas a distance measurement device. Alternatively, buttons or switches maybe provided on the control device 18 to manually set the distance to thetarget from the head mounted display.

A description will be given below of the adjustment of the convergenceangle commensurate with the distance to the target from the head mounteddisplay with reference to FIG. 10B. Here, “a” is the virtual imagedistance of the image (text) displayed by the image display devicesbased on the second image signal, and “α” is the convergence angle tothe image at this time. Further, “γ” is the convergence angle to theimage when the virtual image position is moved farther by distance “c”from the virtual image distance “a,” and “β” is the convergence angle tothe image when the virtual image position is moved closer by distance“b.” Still further, “D” is the distance between the left and right eyes.Here, assuming that

D=61.5 mm and

a=4000 mm, thenα=53 minutes (53′).

One pixel in the image forming device is defined to be three minutes(3′). Here, if the image display position is moved horizontally andinward by one pixel from the predetermined position, then

β=56 minutes (56′), andb=225 mm. On the other hand, if the image display position is movedhorizontally and outward by one pixel from the predetermined position,γ=50 minutes (50′), andc=228 mm. Further, assuming a=8000 mm, moving the image by one pixelmoves the virtual image distance by about 1 m.

As described above, the convergence angle can be adjusted byhorizontally moving the image display position from the predeterminedposition. In other words, the second image signal is controlled that issupplied to the image forming devices 111A and 111B making up the twoimage display devices 100, 200, 300, 400 or 500 for the right and lefteyes by using not only the display position control signal but also theconvergence angle control signal, thus making it possible to accuratelyadjust the convergence angle commensurate with the distance to thetarget from the head mounted display. This brings the distance betweenthe target and viewer (audience) 40 into agreement or as close agreementas possible with the virtual image distance of the image (e.g., text)displayed by the image display devices, thus allowing for the viewer(audience) 40 watching the target to naturally watch the image displayedby the image display devices without significantly changing the focus.

It should be noted that controlling the first image signal describedearlier basically provides the same change in image as described above,thus making it possible to find a display position control signal.

A luminance signal of an image to be displayed on the optical devicescan be transmitted to the head mounted display from external equipmentin addition to the image signal (second image signal) supplied to theimage forming devices, so visibility of the displayed image can beenhanced. Alternatively, the head mounted display can further include alight reception sensor so that the luminance of the image to bedisplayed on the optical devices can be controlled based on luminanceinformation of the environment (atmosphere in which the head mounteddisplay or target is located) obtained by the light reception sensor.More specifically, among examples of the light reception sensor are aphotodiode and a light reception element for exposure measurementincorporated in the imaging device 17.

When the head mounted display is used, for example, at a theater, it isonly necessary to display, on the head mounted display, explanatory textfor describing the content, progress, background and other informationof a play and so on. However, the virtual image distance must be adesired distance. That is, the distance between the target and viewer(audience) and the virtual image distance of the image (e.g., text)displayed by the image display devices change depending on where theviewer is seated. As a result, it is necessary to optimize the virtualimage distance dependently on the viewer's position. In the head mounteddisplay in example 1, however, the convergence angle is optimizedcommensurate with the distance to the target from the head mounteddisplay, thus optimizing the virtual image distance dependently on theviewer's position. Further, there are cases where one wishes to changethe virtual image distance depending on the scene. In such a case, thevirtual image distance can be readily changed by transmitting thedistance information from the head mounted display to the target to thehead mounted display from external equipment.

Alternatively, the viewer (user) can set a desired virtual imagedistance or position. More specifically, switches or buttons areprovided on the control device 18. The viewer can place the virtualimage at a desired distance or position by manipulating the switches orbuttons by himself or herself. For example, if the background changes,the virtual image distance or position can be changed as desired. Such atask is need only be performed as appropriate, for example, duringviewing of the target, and may be performed by the viewer and such atask is more specifically composed of causing the control device 18 toadd the convergence angle control signal to the second image signal.This allows for the viewer, for example, to positively read the textsuch as subtitles without significantly changing his or her line ofsight. Further, it is possible to readily and simultaneously displaysubtitles or other information suited to each of the viewers (e.g.,subtitles or other information in different languages).

Here, the second image signal is digital data and prepared in advancebefore being displayed. The image display position need only be setwhere it does not obstruct the viewing of the target. More specifically,on the other hand, image display is achieved by transmitting the secondimage signal to the control device 18 from the text data wirelesstransmission device 52, for example, based on the predetermined scheduleor time allocation or according to the progress of the target and undercontrol of the computer (not shown) incorporated in the text datareproduction device 51 or image data/text data reproduction device 51′.

In the head mounted display in example 1, if the second image signalcontains not only text data but also luminance data and chromaticitydata relating to text to be displayed, it is possible to positivelyprevent text such as subtitles from becoming difficult to visuallyidentify dependently on the background of the text. It should be notedthat luminance data for the luminance of a predetermined region (e.g.,region corresponding to one third of the bottom of the stage) includingthe targets (e.g., characters and background) as seen through the imagedisplay devices is among examples of luminance data. On the other hand,chromaticity data for the chromaticity of a predetermined regionincluding the targets as seen through the image display devices is amongexamples of chromaticity data. In particular, unless the balance betweenthe brightness of, for example, the screen or stage as seen through asee-through optical device and the brightness and color of the textdisplayed on the optical device falls within a given range, it maybecome difficult to view subtitles, screen, stage and so on in afavorable manner. However, the head mounted display in example 1 cantailor the brightness and color of text to be displayed to match thescreen, stage and so on, thus making the text readily visuallyidentifiable. That is, it is possible to positively prevent text, forexample, for describing the targets viewed by the viewer (audience) frombecoming difficult to visually identify dependently on the background ofthe text. Then, when the head mounted display in example 1 is used, forexample, to view a play, it is only necessary to display text relatingto the targets (e.g., explanatory text relating to the situation behindand background of the play, explanatory text about the characters andconversations of the characters) on the image display devices 100, 200,300, 400 or 500. More specifically, it is only necessary, for example,to transmit text data to the image display devices 100, 200, 300, 400 or500 by the manipulation of the worker or under control, for example, ofa computer so as to display the text on the image display devices 100,200, 300, 400 or 500.

Further, it is said that a fixed virtual image position causes eyefatigue. The reason for this is that a fixed focus leads to less eyeballmovement. Therefore, changing the virtual image distance or moving thevirtual image position properly is effective in reducing eye fatigue.That is, the position of the virtual image formed by the two opticaldevices or the distance to the virtual image formed by the two opticaldevices from the two optical devices (virtual image distance) may bechanged over time. More specifically, it is only necessary to change,for example, every five minutes, the horizontal position of the image,for example, by two pixels in the positive direction on the imageforming device, for example, for a period of one minute, and thenrestore the image to its original position.

As described above, the method in example 1 controls the first imagesignal supplied to the image forming device making up at least one ofthe image display devices, thus controlling the position of the imagedisplayed on the optical device making up at least one of the imagedisplay devices and thereby adjusting the mutual positions of the twoimages. This makes it possible to optically adjust, with ease, the twoimage display devices for the right and left eyes, i.e., adjust, withease, the optical positions of the two image display devices so as toprovide a desired image, for example, during manufacture of a binocularhead mounted display.

Example 2

Example 2 is a modification of the image display device in example 1. Asillustrated in FIGS. 11 and 13 showing, respectively, conceptualdiagrams of the image display devices 200 and 400 of the head mounteddisplays in example 2 and example 4 which will be described later, theimage forming device 211 includes an image forming device having asecond configuration. That is, the image forming device 211 includes alight source 251 and a scanning section 253 adapted to scan parallelbeams emitted from the light source 251. More specifically, the imageforming device 211 includes the light source 251, a collimating optics252, the scanning section 253 and relay optics 254. The collimatingoptics 252 shapes light, emitted from the light source 251, intoparallel beams. The scanning section 253 scans the parallel beamsemitted from the collimating optics 252. The relay optics 254 relays andemits the parallel beams scanned by the scanning section 253. It shouldbe noted that the image forming device 211, as a whole, is housed in anenclosure 213 (shown by a long dashed short dashed line in FIGS. 11 and13). The enclosure 213 has an opening (not shown) so that light isemitted from the relay optics 254 via the opening. Each of theenclosures 213 is attached to one of the temple portions 13 by theattachment member 19.

The light source 251 includes a light-emitting element adapted to emitwhite light. Light emitted from the light source 251 enters thecollimating optics 252 having, as a whole, positive optical power. Lightis emitted from the collimating optics 252 in the form of parallelbeams. These parallel beams are reflected by a total reflection mirror256 and then scanned horizontally and vertically by the scanning section253 to form a kind of two-dimensional image, thus generating virtualimages (number of pixels may be, for example, the same as in example 1).The scanning section 253 includes a MEMS device which is atwo-dimensionally rotatable micromirror capable of scanning incidentparallel beams two-dimensionally. Light from the virtual pixels passesthrough the relay optics (parallel beam emission optics) 254, afterwhich light flux shaped into parallel beams enters the optical device120. The relay optics 254 includes a well-known relay optics.

The optical device 120, adapted to receive light flux shaped intoparallel beams by the relay optics 254, guide it therein and emit it,has the same configuration and structure as the optical device describedin example 1. Therefore, the detailed description thereof is omitted. Onthe other hand, the head mounted display in example 2 has the sameconfiguration and structure as that in example 1 except for the abovedifferences. Therefore, the detailed description thereof is omitted.

Example 3

Example 3 is also a modification of the image display device inexample 1. FIG. 12A illustrates a conceptual diagram of the imagedisplay device 300 of the head mounted display in example 3. FIG. 12Billustrates a schematic sectional view showing, in an enlarged fashion,part of a reflection volume holographic diffraction grating. In example3, the image forming device 111 includes an image forming device havinga first configuration as in example 1. On the other hand, the opticaldevice 320 has the same basic configuration and structure as the opticaldevice 120 in example 1 except for the differences in configuration andstructure of the first and second deflection section.

In example 3, the first and second deflection section are provided onthe front surface of the light guide plate 321 (more specifically, thesecond surface 323 of the light guide plate 321). The first deflectionsection diffracts incident light on the light guide plate 321, and thesecond deflection section diffracts, a plurality of times, light thathas propagated in the light guide plate 321 by total reflection. Here,the first and second deflection section each include a diffractiongrating element and specifically a reflection diffraction gratingelement, and more specifically a reflection volume holographicdiffraction grating. In the description given below, the firstdeflection section including a reflection volume holographic diffractiongrating will be referred to as a “first diffraction grating member 330”for convenience, and the second deflection section including areflection volume holographic diffraction grating will be referred to asa “second diffraction grating member 340” for convenience.

In example 3 or in example 4 which will be described later, the firstand second diffraction grating members 330 and 340 each include a singlelayer of diffraction grating. It should be noted that interferencefringes for one wavelength range (or wavelength) are formed on eachdiffraction grating layer made of a photopolymer material. Theinterference fringes are formed by an existing method. The pitch betweenthe interference fringes formed on the diffraction grating layer(diffraction optical element) is constant. The interference fringes arelinear and parallel to the Z axis. It should be noted that the axes ofthe first and second diffraction grating members 330 and 340 areparallel to the X axis, and that the normals thereof are parallel to theY axis.

FIG. 12B illustrates a schematic partial sectional view showing, in anenlarged fashion, a reflection volume holographic diffraction grating.Interference fringes having a slant angle φ are formed on the reflectionvolume holographic diffraction grating. Here, the term “slant angle φ”refers to the angle formed between the surface of the reflection volumeholographic diffraction grating and interference fringes. Theinterference fringes are formed on the reflection volume holographicdiffraction grating from the inside to the surface thereof. Theinterference fringes satisfy the Bragg condition. Here, the term “Braggcondition” refers to the condition in which Equation (A) is satisfied.In Equation (A), m is a positive integer, λ is the wavelength, d is thegrating surface pitch (spacing between the virtual planes each includingan interference fringe along the normal), and Θ is the complementaryangle of the incidence angle of light on the interference fringes.Further, when light finds its way into the diffraction grating member atan incidence angle ψ, the relationship between Θ, the slant angle φ andthe incidence angle ψ is as shown in Equation (B).

m·λ=2·d·sin(Θ)  (A)

Θ=90°−(φ+ψ)  (B)

The first diffraction grating member 330 is provided on (bonded to) thesecond surface 323 of the light guide plate 321 as described earlier.The first diffraction grating member 330 reflects or diffracts theparallel beams incident on the light guide plate 321 so that theincident parallel beams are totally reflected in the light guide plate321. Further, the second diffraction grating member 340 reflects ordiffracts, a plurality of times, the parallel beams that have propagatedin the light guide plate 321 by total reflection and emits the beamsfrom the first surface 322 of the light guide plate 321 still in theform of parallel beams.

The light guide plate 321 emits the parallel beams that have propagatedtherein by total reflection. At this time, the number of times theparallel beams are totally reflected before reaching the seconddiffraction grating member 340 differs depending on the angle of viewbecause the light guide plate 321 is thin and because the optical pathin the light guide plate 321 is long. More specifically, of the parallelbeams incident on the light guide plate 321, the number of times ofreflection of those incident at an angle in the direction of approachingthe second diffraction grating member 340 is smaller than that of thoseincident at an angle in the direction of distancing from the seconddiffraction grating member 340. The reason for this is that the parallelbeam diffracted or reflected by the first diffraction grating member 330and incident on the light guide plate 321 at an angle in the directionof approaching the second diffraction grating member 340 forms a smallerangle with the normal of the light guide plate 321 when striking theinner surface of the light guide plate 321 during propagation in thelight guide plate 321 than that incident on the light guide plate 321 atan angle in the opposite direction. Further, the shape of theinterference fringes formed in the second diffraction grating member 340and that of the interference fringes formed in the first diffractiongrating member 330 are symmetrical with respect to the virtual planevertical to the axis of the light guide plate 321.

The light guide plate 321 in example 4 which will be described later hasthe same configuration and structure as the light guide plate 321described above. The head mounted display in example 3 has the sameconfiguration and structure as that in example 1 except for the abovedifferences. Therefore, the detailed description thereof is omitted.

Example 4

Example 4 is a modification of the image display device in example 3.FIG. 13 illustrates a conceptual diagram of the image display device ofthe head mounted display in example 4. The light source 251, collimatingoptics 252, scanning section 253, parallel beam emission optics (relayoptics) 254 and other components of each of the image display devices400 have the same configuration and structure as their counterparts inexample 2 (image forming device having a second configuration). On theother hand, the optical device 320 in example 4 has the sameconfiguration and structure as that in example 3. The head mounteddisplay in example 4 has the same configuration and structure as thosein examples 1 and 2 except for the above differences. Therefore, thedetailed description thereof is omitted.

Example 5

Example 5 is a modification of the image display devices in examples 1to 4. FIGS. 14A and 14B illustrate conceptual diagrams of thearrangement of the light guide plate and other components making up theimage display device of the head mounted display in example 5. FIG. 15illustrates a schematic diagram of the head mounted display in example 5as seen from the side.

In examples 1 to 4, the central beam CL, emitted from the center of theimage forming device 111 or 211 and passing through the node of theoptics 112 or 254 on the side of the image forming device, is designedto vertically strike the light guide plate 121 or 321 in the imagedisplay devices 100 or 300 as illustrated in FIG. 2. That is, thecentral beam CL is designed to enter the light guide plate 121 or 321 ata zero incidence angle. In this case, the center of the displayed imagematches the vertical direction of the first surface 122 or 322 of thelight guide plate 121 or 321.

That is, in an image display device as typified by the image displaydevice 100, the central beam CL emitted from the center of the imageforming device 111 located in the optical axis of the collimating optics112 is converted first into an approximately parallel beam by thecollimating optics 112 and then vertically enters the first surface(incidence surface) 122 of the light guide plate 121 as illustrated inFIG. 2. Then, the beam proceeds along a propagation direction A while atthe same time being totally reflected between the first and secondsurfaces 122 and 123 by the first deflection section 130. Next, thecentral beam CL is reflected or diffracted by the second deflectionsection 140 and emitted vertically from the first surface 122 of thelight guide plate 121, thus reaching the eye 41 of the viewer(audience).

In order to prevent the optical device 120, 320 or 520 from obstructingthe viewing of the horizontally located target by the viewer (audience)in a see-through head mounted display, it is preferred that the opticaldevice 120, 320 or 520 should be provided slightly lower than thehorizontal line of sight of the viewer. In such a case, the imagedisplay devices 100 or 300, as a whole, is provided lower than thehorizontal line of sight of the viewer. Incidentally, in such aconfiguration, the image display device 100 as a whole must be tilted byangle θ as illustrated in FIG. 20. This leads to the limitation of theangle θ at which the image display device 100 can be tilted or a lowerdegree of design freedom because of the relationship with the attachmentportion (temple portion) of the eyeglass type frame for wearing on thehead of the viewer. Therefore, it is further preferred that the imagedisplay devices should allow for arrangement with a high degree offreedom and offer a high degree of design freedom.

In example 5, the central beam CL intersects the XY plane at angle θother than zero degree. Further, the central beam CL is included in theYZ plane. Still further, in example 5 or example 6 which will bedescribed later, the optical axis of the optics 112 or 254 is includedin the YZ plane and intersects the XY plane at an angle other than zerodegree, and more specifically, at angle θ (refer to FIGS. 14A and 14B).Further, in example 5 or example 6 which will be described later,assuming that the XY plane matches the horizontal plane, the angle θ atwhich the central beam CL intersects the XY plane is an elevation angle.That is, the central beam CL proceeds toward the XY plane from under thesame plane to strike the same plane. Then, the XY plane intersects thevertical plane at an angle other than zero degree, and morespecifically, at angle θ.

In example 5, θ is five degrees. More specifically, the central beam CL(shown by a dotted line in FIG. 15) is included in the horizontal plane.Then, the optical device 120, 320 or 520 is tilted relative to thevertical plane by an angle θ. In other words, the optical device 120,320 or 520 is tilted relative to the horizontal plane by an angle of(90−θ) degrees. Further, a central beam CL′ (shown by a long dashedshort dashed line in FIG. 15) emitted from the optical device 120, 320or 520 is tilted relative to the horizontal plane by an angle 2θ. Thatis, when the viewer watches the target at an infinitely distant place inthe horizontal direction, the central beam CL′ emitted from the opticaldevice 120, 320 or 520 and enters the eyes of the viewer forms adepression angle θ′ (=2θ) (refer to FIG. 15). The angle formed betweenthe central beam CL′ and the normal of the optical device 120, 320 or520 is θ. In FIG. 14A or FIG. 16A which will be described later, thepoint where the central beam CL′ is emitted from the optical device 120,320 or 520 is denoted by O′, and the axes that pass through the point O′and are parallel to the X, Y and Z axes are denoted respectively by theX′, Y′ and Z′ axes.

In the image display devices in example 5, the central beam CLintersects the XY plane at the angle (θ) other than zero degree. Here,the central beam CL′ that is emitted from the optical device and entersthe eyes of the viewer (audience) forms a depression angle θ′ where thefollowing relationship holds: θ′=2θ

In the example shown in FIG. 20, on the other hand, the image displaydevice as a whole need be tilted by an angle θ″ to provide the samedepression angle. Here, the following relationship holds between θ″ andθ:

θ″=2θ

As a result, the optical device must be tilted relative to the verticalaxis by 2θ in the example shown in FIG. 20. In example 5, on the otherhand, it is only necessary to tilt the optical device relative to thevertical axis by θ and maintain the image forming device horizontal.Therefore, the limitation on the angle at which the image display deviceis to be attached to the attachment portion of the eyeglass type frameis less stringent, thus providing a high degree of design freedom.Further, the optical device is tilted less relative to the verticalsurface than in the example shown in FIG. 20, thus making it unlikelythat external light may be reflected by the optical device to enter theeye of the viewer (audience). This provides high quality image display.

The head mounted display in example 5 has the same configuration andstructure as those in examples 1 to 4 except for the above differences.Therefore, the detailed description thereof is omitted.

Example 6

Example 6 is a modification of the image display device in example 5.FIGS. 16A and 16B are conceptual diagrams of the arrangement of thelight guide plate and other components making up the image displaydevice in example 6. Here, in example 6, the optical axis of the optics(parallel beam emission optics or collimating optics) 112 is parallel tothe YZ and XY planes and passes through a position off the center of theimage forming device 111. Thanks to such a configuration, the centralbeam CL is included in the YZ plane and intersects the XY plane at theelevation angle θ. The head mounted display in example 6 has the sameconfiguration and structure as those in examples 1 to 5 except for theabove differences. Therefore, the detailed description thereof isomitted.

Example 7

Example 7 is also a modification of the image display device inexample 1. FIG. 17 illustrates a schematic diagram of the head mounteddisplay in example 7 as seen from the front. FIG. 18 illustrates aschematic diagram of the head mounted display in example 7 as seen fromabove.

In example 7, the optical devices 520 each include a half mirror adaptedto receive light emitted from the image forming device 111A or 111B andemit light toward the eye 41 of the viewer 40. It should be noted thatlight emitted from the image forming device 111A or 111B propagates in atransparent member 521 such as glass plate or plastic plate and enterthe optical device 520 (half mirror). Alternatively, however, lightemitted from the image forming device 111A or 111B may propagate in theair and enter the optical device 520 (half mirror). Still alternatively,the image forming devices 211 described in example 2 may be used asimage forming devices.

Each of the image forming devices 111A and 111B is, for example, screwedto the front portion 11. Further, the transparent member 521 is attachedto each of the image forming devices 111A and 111B, and the opticaldevice 520 (half mirror) is attached to each of the transparent members521. The head mounted display in example 7 has the same configurationand structure as those in examples 1 to 6 except for the abovedifferences. Therefore, the detailed description thereof is omitted.

Example 8

Example 8 relates to the optical position adjustment methods of a headmounted display according to the third and fourth embodiments. FIG. 19illustrates a schematic diagram of the head mounted display in example 8as seen from above for describing the optical position adjustment methodof a head mounted display.

In example 8, the images to be displayed on the optical devices 120, 320or 520 are captured with imaging devices (cameras) 61A and 61B. Theimages obtained by the imaging devices 61A and 61B are, for example,those shown in FIG. 9A, 9B or 9C. Then, the displacements of the imagesobtained by the imaging devices 61A and 61B from reference positions arefound.

Here, the term “reference positions” refers to the image capturepositions of the imaging devices (cameras) 61A and 61B whenpredetermined images displayed on the optical devices 120, 320 or 520are captured with the associated imaging devices (cameras) 61A and 61Bassuming that the image forming devices 111 or 211 are attached at thecorrect positions. The predetermined images can be obtained bytransmitting, to the control device 18, an image signal (input imagesignal or input image data) serving as a first image signal that allowsfor a kind of test pattern to be displayed, processing the first imagesignal in the control device 18 for image display and generating theimage in the image forming devices. If the image forming devices 111 or211 are attached at incorrect positions, the image capture positionsobtained by the imaging devices (cameras) 61A and 61B when thepredetermined images displayed on the optical devices 120, 320 or 520are captured with the associated imaging devices (cameras) 61A and 61Bare displaced from the reference positions.

Tasks adapted to eliminate the displacement may be performed by thecontrol device 18 or an external computer connected to the controldevice 18. The first image signal is controlled that is supplied to theimage forming device 111 or 211 making up at least one of the imagedisplay devices so as to eliminate the displacement, thus adjusting themutual positions of the two images as in example 1. That is, a displayposition correction signal is found that eliminates the displacement.More specifically, a worker manipulates the switches or buttons on thecontrol device 18 to move the test pattern horizontally and verticallyand rotating it, thus overlaying the image on the reference position.Then, it is only necessary to find and determine the display positioncorrection signal based on the horizontal, vertical and rotary movementswhen the image is overlaid on the reference position. Alternatively, ifthe horizontal, vertical and rotary displacements of the image from thereference position are found by a computer, these displacements serve asa display position correction signal adapted to overlay the image on thereference position. Then, this display position correction signal isstored in the control device as a display position control signal.

Except for the above, the optical position adjustment method of a headmounted display in example 8 is substantially identical to thatdescribed in example 1. Therefore, the detailed description thereof isomitted. On the other hand, the configuration and structure of the headmounted display in example 8 need only be the same as those described inexamples 1 to 7. Therefore, the detailed description thereof is omitted.

Example 9

Example 9 is a modification of the image display device in example 8. Inexample 9, the reference positions are set to the subject imagingpositions of the imaging devices 61A and 61B when a subject provided ata predetermined position forward of the two optical devices 120, 320 or520 is imaged by the imaging devices 61A and 61B. More specifically, acrosshair graphic as illustrated, for example, on the left of FIG. 9C isprovided, for example, 4 m forward of the two optical devices 120, 320or 520 as a subject. On the other hand, the predetermined image(crosshair graphic) is displayed on the two optical devices 120, 320 or520. Here, the virtual image distance of the predetermined image is alsoset, for example, to 4 m. That is, an image signal (input image signalor input image data) serving as a first image signal that allows for akind of test pattern to be displayed is transmitted to the controldevice 18 and processed by the control device 18 for image display, thusdisplaying the predetermined image on the image forming devices. At thesame time, the predetermined images displayed on the optical devices120, 320 or 520 are captured with the associated imaging devices(cameras) 61A and 61B to obtain the subject imaging positions.

Then, the first image signal is controlled that is supplied to the imageforming device 111 or 211 making up at least one of the image displaydevices by the control device 18 or an external computer connected tothe control device 18 so that the images obtained by capturing thesubject and those displayed on the optical devices 120, 320 or 520 aresuperimposed one on top of another, that is, so that the subject imagingpositions match the image capture positions, thus adjusting the mutualpositions of the two images as in example 8. That is, a display positioncorrection signal adapted to eliminate the displacement is found byperforming the same tasks and following the same method as described inexample 8. Then, this display position correction signal is stored inthe control device as a display position control signal.

Although the present invention has been described above based on thepreferred embodiments, the present invention is not limited thereto. Theconfigurations and structures of the head mounted display and imagedisplay devices are merely illustrative and may be changed asappropriate. For example, a surface relief hologram (refer to US PatentNo. 20040062505A1) may be used as a light guide plate. The opticaldevice 320 in example 3 or 4 may include a transmission diffractiongrating element. Alternatively, one of the first and second deflectionsections may include a reflection diffraction grating element, and theother may include a transmission diffraction grating element. Stillalternatively, blazed reflection diffraction grating elements may beused as diffraction grating elements.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2010-089494 filedin the Japan Patent Office on Apr. 8, 2010, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factor in so far as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A display apparatus, including: an image formingdevice; and an optical device configured to reflect light emitted fromthe image forming device, wherein the image forming device is configuredto control an image signal for display by the optical device accordingto a distance from a viewer to a target such that a convergence angle ofthe viewer can be adjusted with the distance from the viewer to thetarget.
 2. The display apparatus of claim 1, wherein the image formingdevice is configured to control a received image signal so as to controla position of an image displayed by the optical device of the imagedisplay device and adjust a position of the image.
 3. The displayapparatus of claim 1, wherein the image forming device is configured toadjust the position of the image by a combination of horizontal andvertical movements and rotation of the image displayed on the opticaldevice of the image display device.
 4. The display apparatus of claim 1,wherein the optical device is see-through.
 5. The display apparatus ofclaim 1, wherein the distance from the viewer to the target is providedat least in part via information transmitted to the display apparatusfrom an external equipment.
 6. The display apparatus of claim 1, furthercomprising a distance measurement device adapted to obtain distanceinformation by measuring the distance to the target from the viewer. 7.The display apparatus of claim 1, further comprising a light receptionsensor for obtaining environment luminance information, wherein theimage forming device is configured to control a luminance of the imagesignal based at least in part on the environment luminance information.8. The display apparatus of claim 1, wherein the image forming device isconfigured to control the image signal to comprise text based at leastin part on the distance from the viewer to the target.
 9. The displayapparatus of claim 1, wherein the image forming device is configuredcontrol the image signal so that a position of a virtual image formed bythe optical device changes over time.
 10. The display apparatus of claim9, wherein the position of the virtual image is changed to reduce aviewer's eye fatigue.
 11. The display apparatus of claim 9, wherein theposition of the virtual image is changed according to a predeterminedschedule.
 12. The display apparatus of claim 9, wherein the position ofthe virtual image is changed in a horizontal direction.
 13. The displayapparatus of claim 1, wherein the image forming device comprises adigital micromirror device (DMD).
 14. The display apparatus of claim 1,wherein the image forming device comprises a Micro Electro MechanicalSystems (MEMS).
 15. The display apparatus of claim 1, wherein the imageforming device comprises a laser element.
 16. A display apparatuscomprising: an image display device, configured to control a receivedimage signal based at least in part on a distance from a viewer to atarget, and wherein a position of a virtual image formed by the imagedisplay device is changed over time.
 17. The display apparatus of claim16, wherein the position of the virtual image is changed according to apredetermined schedule.
 18. The display apparatus of claim 16, whereinthe position of the virtual image is changed in a horizontal direction.19. The display apparatus of claim 16, wherein the image display devicecomprises a digital micromirror device (DMD).
 20. The display apparatusof claim 16, wherein the image display device comprises a Micro ElectroMechanical Systems (MEMS).
 21. The display apparatus of claim 16,wherein the image display device comprises a laser element.
 22. Adisplay apparatus comprising: an image display device, configured tocontrol a received image signal based at least in part on a distancefrom an viewer to a target, and wherein a distance to a virtual imageformed by the image display device is changed over time.
 23. The displayapparatus of claim 22, wherein the distance of the virtual image ischanged according to a predetermined schedule.
 24. The display apparatusof claim 22, wherein the image display device comprises a digitalmicromirror device (DMD).
 25. The display apparatus of claim 22, whereinthe image display device comprises a Micro Electro Mechanical Systems(MEMS).
 26. The display apparatus of claim 22, wherein the image displaydevice comprises a laser element.